I could send you a copy of mine if you like the look of it. It's a Google Docs spreadsheet so that it can update prices automatically -- it could be exported to Excel, but the automatic price updating would be lost. I've heard there are ways to do automatic price updating in Excel, but I haven't messed with it.
Only the blue cells are edited directly; everything else is calculated from them. Column H has several levels of conditional formatting going from yellow to red as things dirft further out of balance. If you're not using ETFs and don't have to worry about rounding off to the nearest share, some of the columns could be deleted.